1. Field of the Invention
This invention generally relates to a structure formed on a sprocket to aid in shifting of a bicycle chain. More specifically, the present invention relates to a sprocket assembly with more projections formed on a sprocket to aid in shifting the bicycle chain from a smaller sprocket to a larger sprocket.
2. Background Information
In a multi-stage sprocket assembly of a bicycle having a derailleur, a chain is movable by a shifting force of the derailleur from a small sprocket to a large sprocket. In a conventional sprocket assembly, a side surface of the chain contacts a side surface of the large sprocket, and the chain is supported by the large sprocket through a frictional force produced by the contact. With rotation of the large sprocket, the chain is raised radially outwardly of this sprocket to engage teeth of the sprocket.
However, shifting of the chain in this manner requires a sufficient frictional force produced between the chain and the large sprocket to pick up the chain reliably with rotation of the sprocket. In other words, the derailleur must exert a strong force to press the chain upon the large sprocket.
When a heavy drive load occurs during a shifting operation, the chain may slip from the large sprocket. This makes it very difficult to pick up the chain with the large sprocket, or results in a delay of chain shift. In order to overcome this problem, Shimano Inc., the assignee of this subject application, has developed a sprocket assembly with projections that aid in the shifting of the bicycle chain as disclosed in U.S. Pat. No. 5,413,534 to Nagano. The entire disclosure of U.S. Pat. No. 5,413,534 is hereby incorporated herein by reference. While the sprocket assembly disclosed in this Shimano patent operates very well in shifting the chain from a smaller sprocket to a larger sprocket, the projections on the larger sprocket sometimes causes a slight obstruction during the shifting. In other words, this obstruction caused by the projections can make the gear-changing operation unsteady and produce an unsatisfactory sensation to the rider.
In view of the above, there exists a need for an improved sprocket assembly which overcomes the above mentioned problems in the prior art. This invention addresses this need in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.
One object of the present invention is to provide a sprocket assembly that provides a smooth shifting action between a small sprocket to a large sprocket.
An object of the present invention is to provide a sprocket structure for shifting a chain from a small sprocket to a large sprocket relatively easily, and that reliably even under a heavy drive load.
The foregoing objects of the present invention are basically attained by providing a sprocket assembly with improved projections on the larger sprocket.
The foregoing objects of the present invention can also be attained by providing a sprocket assembly for a bicycle comprising a small sprocket and a large sprocket. The small sprocket has a plurality of circumferentially spaced teeth. The large sprocket has a plurality of circumferentially spaced teeth and at least one first chain support projection located on a side surface of the large sprocket that faces toward the small sprocket. The first chain support projection includes a contact surface for contacting a lower surface of an outer link plate of a chain shifted from the small sprocket to the large sprocket. The first chain support projection is oriented and sized to slip between a pair of adjacent outer link plates. The first chain support projection is disposed adjacent the teeth of the large sprocket to cause the contact surface to contact the chain engaged with the small sprocket and pick up the chain radially outward relative to a center of rotation of the large sprocket during a chain shift from the small sprocket to the large sprocket.
The foregoing objects can also be attained by providing a large sprocket for a bicycle with improved projections. The sprocket comprises a plurality of circumferentially spaced teeth, and at least one first chain support projection located on a side surface of the large sprocket that faces toward an adjacent small sprocket. The first chain support projection includes a contact surface for contacting a lower surface of an outer link plate of a chain shifted from the adjacent small sprocket to the large sprocket. The first chain support projection is oriented and sized to slip between a pair of adjacent outer link plates. The first chain support projection is disposed adjacent the teeth of the large sprocket to cause the contact surface to contact the chain engaged with the adjacent small sprocket and pick up the chain radially outward relative to a center of rotation of the large sprocket during a chain shift from the adjacent small sprocket to the large sprocket.
These and other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention.